The present invention relates to a semiconductor memory device, and more particularly to a semiconductor memory device having a data mask function.
The data mask function of a semiconductor memory device is used when it is desirable to prevent input data from being written to a memory cell. The data is generally masked in an 8-bit unit. In other words, one mask pin is provided for 8 data input/output pins (DQ).
Accordingly, two data mask signals are used for a semiconductor memory device having an ‘x16’ structure and four data mask signals are used for a semiconductor memory device having an ‘x32’ structure. Furthermore, a single data mask signal is used for a semiconductor memory device having ‘x8’ and ‘x4’ structures.
In a semiconductor memory device according to the prior art, a write driver is arranged for each data line. Therefore, as illustrated in FIG. 1, eight write drivers 10 are arranged with each corresponding to one of eight global data lines GIO<0:7>, and the eight write drivers 10 share one data mask signal DM.
In addition, the write drivers 10 transmit data of the global data lines GIO<0:7> to respective local data lines LIO<0:7> and LIOB<0:7> according to a write command signal WT_CMD. When a data mask signal DM is in an enable state, the data is masked and not transmitted to local data lines LIO<0:7> and LIOB<0:7>.
As illustrated in FIG. 2, a representative configuration of a write driver 10 connected to a global data line GIO<0> may include a driving control unit 20 and a driving unit 22.
The write driver 10 operates such that if the data mask signal DM is in a disable state when a write command signal WT_CMD is inputted to a driving control unit 20, a driving control signal DRV is enabled. Accordingly, a data of a global data line (for instance GIO<0>) is transmitted to a local data line LIO<0> and LIOB<0> via a driving unit 22.
On the other hand, if the data mask signal DM is in an enable state, a driving control signal DRV is disabled via a driving control unit 20. Accordingly, a data of a global data line (for instance GIO<0>) is masked and not transmitted to a local data line LIO<0> and LIOB<0> through a driving unit 22.
In the semiconductor memory device according to the prior art as described above, the write driver 10 having the configuration as illustrated in FIG. 2 is arranged for each data line to control a data transmission or mask for each data line.
However, as semiconductor memory devices process larger amounts of data at faster speeds, the number of data lines may increase. According to the prior art, a write driver is arranged for each data line. Therefore, the number of write drivers increases according to the increased number of data lines.
Such an increased number of write drivers causes a problem in that increased current consumption may occur due to a data mask operation of the write drivers. Another problem may occur in that the area occupied by the write drivers in each bank is increased, thereby increasing the overall layout area of a semiconductor chip.